College Physics (4th Edition)

Published by McGraw-Hill Education
ISBN 10: 0073512141
ISBN 13: 978-0-07351-214-3

Chapter 4 - Problems - Page 151: 64


(a) The elevator's upward acceleration is $2.2~m/s^2$ (b) Luke's weight is $784~N$

Work Step by Step

(a) The apparent weight of the box is $1200~N-960~N = 240~N$ We can find the upward acceleration: $F_N - mg = ma$ $a = \frac{F_N-mg}{m}$ $a = \frac{240~N-(20.0~kg)(9.80~m/s^2)}{20.0~kg}$ $a = 2.2~m/s^2$ The elevator's upward acceleration is $2.2~m/s^2$ (b) We can find Luke's mass: $F_N - mg = ma$ $F_N = m~(g+a)$ $m = \frac{F_N}{g+a}$ $m = \frac{960~N}{9.80~m/s^2+2.2~m/s^2}$ $m = 80~kg$ Luke's weight is $(80~kg)(9.80~m/s^2) = 784~N$
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